Shauna Lawhorne, with Chemical Safety Board public affairs, displays photos on Monday, August 20, 2012 in Richmond, Calif., of the vapor cloud at the Chevron refinery that exploded on Aug. 6. Photo: Carlos Avila Gonzalez, The Chronicle / SF less

Shauna Lawhorne, with Chemical Safety Board public affairs, displays photos on Monday, August 20, 2012 in Richmond, Calif., of the vapor cloud at the Chevron refinery that exploded on Aug. 6. Photo: Carlos ... more

Firefighting crews continue to pour water onto a unit after a fire at a Chevron refinery on Tuesday, Aug. 7, 2012 in Richmond, Calif. The fire, which sent plumes of black smoke over the San Francisco Bay area, erupted Monday evening in the massive Chevron refinery about 10 miles (16 kilometers) northeast of San Francisco. It was out early Tuesday. less

Firefighting crews continue to pour water onto a unit after a fire at a Chevron refinery on Tuesday, Aug. 7, 2012 in Richmond, Calif. The fire, which sent plumes of black smoke over the San Francisco Bay area, ... more

Photo: Aric Crabb, AP

Firefighting crews continue to pour water onto a unit after a fire... Photo-3499076.49556 - Houston Chronicle

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Firefighting crews continue to pour water onto a unit after a fire at a Chevron refinery on Tuesday, Aug. 7, 2012 in Richmond, Calif. The fire, which sent plumes of black smoke over the San Francisco Bay area, erupted Monday evening in the massive Chevron refinery about 10 miles (16 kilometers) northeast of San Francisco. It was out early Tuesday. less

Firefighting crews continue to pour water onto a unit after a fire at a Chevron refinery on Tuesday, Aug. 7, 2012 in Richmond, Calif. The fire, which sent plumes of black smoke over the San Francisco Bay area, ... more

Photo: Aric Crabb, AP

Firefighting crews continue to pour water onto a unit after a fire... Photo-3499077.49556 - Houston Chronicle

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Firefighting crews continue to pour water onto a unit after a fire at a Chevron refinery on Tuesday, Aug. 7, 2012 in Richmond, Calif. The fire, which sent plumes of black smoke over the San Francisco Bay area, erupted Monday evening in the massive Chevron refinery about 10 miles (16 kilometers) northeast of San Francisco. It was out early Tuesday. less

Firefighting crews continue to pour water onto a unit after a fire at a Chevron refinery on Tuesday, Aug. 7, 2012 in Richmond, Calif. The fire, which sent plumes of black smoke over the San Francisco Bay area, ... more

Photo: Aric Crabb, AP

Firefighting crews continue to pour water onto a unit after a fire... Photo-3499078.49556 - Houston Chronicle

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White smoke rises from the Chevron refinery during a controlled burn on Tuesday, Aug. 7, 2012, the morning after Monday's toxic fire in Richmond, Calif. An investigation into what caused the fire is ongoing. Heather Kulp, Chevron spokesperson, said the fire was caused by a vapor leak. less

White smoke rises from the Chevron refinery during a controlled burn on Tuesday, Aug. 7, 2012, the morning after Monday's toxic fire in Richmond, Calif. An investigation into what caused the fire is ongoing. ... more

White smoke rises from the Chevron refinery during a controlled burn on Tuesday, Aug. 7, 2012, the morning after Monday's toxic fire in Richmond, Calif. An investigation into what caused the fire is ongoing. Heather Kulp, Chevron spokesperson, said the fire was caused by a vapor leak. less

White smoke rises from the Chevron refinery during a controlled burn on Tuesday, Aug. 7, 2012, the morning after Monday's toxic fire in Richmond, Calif. An investigation into what caused the fire is ongoing. ... more

In this undated photo released by the U.S. Chemical Safety Board, structural damage is shown after the Chevron refinery fire in Richmond, Calif. Structural engineers have deemed the site of a Chevron refinery fire in the San Francisco Bay area hazardous for human entry after looking at the failed pipe that leaked and sent a towering plume of black smoke into the sky. Federal and state investigators are discussing plans for how to make the Richmond site safe so the faulty pipe can be removed for testing. less

In this undated photo released by the U.S. Chemical Safety Board, structural damage is shown after the Chevron refinery fire in Richmond, Calif. Structural engineers have deemed the site of a Chevron refinery ... more

Photo: AP

In this undated photo released by the U.S. Chemical Safety Board,... Photo-3499081.49556 - Houston Chronicle

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In this undated photo released by the U.S. Chemical Safety Board, a pipe is shown after the Chevron refinery fire in Richmond, Calif. Structural engineers have deemed the site of a Chevron refinery fire in the San Francisco Bay area hazardous for human entry after looking at the failed pipe that leaked and sent a towering plume of black smoke into the sky. Federal and state investigators are discussing plans for how to make the Richmond site safe so the faulty pipe can be removed for testing. less

In this undated photo released by the U.S. Chemical Safety Board, a pipe is shown after the Chevron refinery fire in Richmond, Calif. Structural engineers have deemed the site of a Chevron refinery fire in the ... more

Photo: AP

In this undated photo released by the U.S. Chemical Safety Board, a... Photo-3499082.49556 - Houston Chronicle

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In this undated photo released by the U.S. Chemical Safety Board, structural damage is shown after the Chevron refinery fire in Richmond, Calif. Structural engineers have deemed the site of a Chevron refinery fire in the San Francisco Bay area hazardous for human entry after looking at the failed pipe that leaked and sent a towering plume of black smoke into the sky. Federal and state investigators are discussing plans for how to make the Richmond site safe so the faulty pipe can be removed for testing. less

In this undated photo released by the U.S. Chemical Safety Board, structural damage is shown after the Chevron refinery fire in Richmond, Calif. Structural engineers have deemed the site of a Chevron refinery ... more

Photo: AP

In this undated photo released by the U.S. Chemical Safety Board,... Photo-3499083.49556 - Houston Chronicle

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Dr. Rafael Moure-Eraso, Chairman of the Chemical Safety Board, addresses the press as they released photos on Monday, August 20, 2012 in Richmond, Calif., of the vapor cloud at the Chevron refinery that exploded on Aug. 6. Photo: Carlos Avila Gonzalez, The Chronicle / SF less

Dr. Rafael Moure-Eraso, Chairman of the Chemical Safety Board, addresses the press as they released photos on Monday, August 20, 2012 in Richmond, Calif., of the vapor cloud at the Chevron refinery that ... more

John Smith, of Richmond, watches the Chevron Oil Refinery fire from a distance through a fence on Castro Road in Richmond, Calif. on Monday, Aug. 6, 2012. Photo: Stephen Lam, Special To The Chronicle / SF

John Smith, of Richmond, watches the Chevron Oil Refinery fire from a distance through a fence on Castro Road in Richmond, Calif. on Monday, Aug. 6, 2012. Photo: Stephen Lam, Special To The Chronicle / SF

A group of teenagers watches smoke and fire from the Chevron Oil Refinery fire in Richmond, Calif. on Monday, Aug. 6, 2012. Photo: Stephen Lam, Special To The Chronicle / SF

A group of teenagers watches smoke and fire from the Chevron Oil Refinery fire in Richmond, Calif. on Monday, Aug. 6, 2012. Photo: Stephen Lam, Special To The Chronicle / SF

A group of teenagers watches smoke and fire from the Chevron Oil... Photo-3499104.49556 - Houston Chronicle

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Smoke and fire from the Chevron Oil Refinery fire as seen in Richmond, Calif. on Monday, Aug. 6, 2012. Photo: Stephen Lam, Special To The Chronicle / SF

Smoke and fire from the Chevron Oil Refinery fire as seen in Richmond, Calif. on Monday, Aug. 6, 2012. Photo: Stephen Lam, Special To The Chronicle / SF

Smoke and fire from the Chevron Oil Refinery fire as seen in... Photo-3499105.49556 - Houston Chronicle

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Flames and smoke shoot up from the Chevron refinery, a fixture in Richmond for more than a century. Photo: John Sebastian Russo, Special To The Chronicle / SF

Flames and smoke shoot up from the Chevron refinery, a fixture in Richmond for more than a century. Photo: John Sebastian Russo, Special To The Chronicle / SF

Flames and smoke shoot up from the Chevron refinery, a fixture in... Photo-3499106.49556 - Houston Chronicle

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Smoke bellows from a fire at the Chevron refinery following an explosion at 6:30 on Monday, August 6, 2012 in Richmond, Calif.Photo: John Sebastian Russo, Special To The Chronicle / SF

Smoke bellows from a fire at the Chevron refinery following an explosion at 6:30 on Monday, August 6, 2012 in Richmond, Calif.
Photo: John Sebastian Russo, Special To The Chronicle / SF

Smoke bellows from a fire at the Chevron refinery following an... Photo-3499107.49556 - Houston Chronicle

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Smoke bellows from a fire at the Chevron refinery following an explosion at 6:30 on Monday, August 6, 2012 in Richmond, Calif.Photo: John Sebastian Russo, Special To The Chronicle / SF

Smoke bellows from a fire at the Chevron refinery following an explosion at 6:30 on Monday, August 6, 2012 in Richmond, Calif.
Photo: John Sebastian Russo, Special To The Chronicle / SF

Smoke bellows from a fire at the Chevron refinery following an... Photo-3499108.49556 - Houston Chronicle

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Marce Gutierrez, of Hercules, watches of plumes of smoke emanate from the Chevron oil refinery on Monday, August 6, 2012 in Richmond, Calif. I'm just trying to figure out if we need to leave, Gutierrez said. Photo: Beck Diefenbach, Special To The Chronicle / SF less

Marce Gutierrez, of Hercules, watches of plumes of smoke emanate from the Chevron oil refinery on Monday, August 6, 2012 in Richmond, Calif. I'm just trying to figure out if we need to leave, Gutierrez said. ... more

Andres Locky takes a photo of himself in front of plumes of smoke emanating from the Chevron oil refinery on Monday, August 6, 2012 in Richmond, Calif. Photo: Beck Diefenbach, Special To The Chronicle / SF

Andres Locky takes a photo of himself in front of plumes of smoke emanating from the Chevron oil refinery on Monday, August 6, 2012 in Richmond, Calif. Photo: Beck Diefenbach, Special To The Chronicle / SF

Andres Locky takes a photo of himself in front of plumes of smoke... Photo-3499110.49556 - Houston Chronicle

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Elizabeth Fein, of El Cerrito, takes a photo of plumes of smoke emanating from the Chevron oil refinery on Monday, August 6, 2012 in Richmond, Calif. Photo: Beck Diefenbach, Special To The Chronicle / SF

Elizabeth Fein, of El Cerrito, takes a photo of plumes of smoke emanating from the Chevron oil refinery on Monday, August 6, 2012 in Richmond, Calif. Photo: Beck Diefenbach, Special To The Chronicle / SF